The present invention is directed, in general to polishing pads for chemical mechanical polishing of semiconductor wafers and integrated circuits. More specifically, the invention is directed to a polishing pad and method for the in situ delivery of slurry modifiers and a polishing apparatus incorporating the present invention.
Chemical-mechanical polishing (CMP) is a popular planarizing technique in the manufacture of VLSI integrated circuits. Although it has potential for planarizing a variety of materials in IC processing, CMP is used most widely for planarizing metallization layers and interlevel dielectrics on semiconductor wafers, and for planarizing substrates for shallow trench isolation.
The success of CMP over other methods, such as etchback, is due to the higher degree of wafer planarity achievable with the CMP technique, as ever-increasing needs for miniaturization in electronic devices require tighter wafer planarity tolerances. In CMP, a semiconductor wafer is polished using a repetitive, regular motion of a mechanical polishing wheel and a slurry which may contain a mixture of fine particles and chemical etchants. By placing the slurry between the polishing wheel and the wafer, material may be removed with a high degree of planarity. To aid in the planarization process, the polishing wheel commonly employs a specialized polishing pad that may be made from felted or woven natural fibers such as wool, or various type of synthetic thermoset polymers, such as urethane-impregnated felted polyester or polyurethane.
There are three critical consumable components in the CMP process. One is the liquid slurry. The slurry""s composition must typically be altered, with special formulations produced for the particular type of substrate being polished. Some substrates, for example, require an alkaline pH to be activated for polishing, while other substrates require an acid environment. Still other substrates respond best to silica abrasives, while others require alumina or titanium abrasive particles. The second critical consumable component in the CMP process is the polishing pad. It must be very flat, uniform across its entire surface and have the right combination of stiffness and compressibility to minimize effects like dishing and erosion. Traditional thinking considers it important that the pad be resistant to the chemical nature of the slurry so as not to decompose during polishing. A third critical consumable component in the CMP process is the carrier film. The carrier film attaches the wafer to its rotating holder, must have an adequately flat and uniform in its thickness, must have an adhesive that will hold it tightly to the carrier but not too tightly to the wafer, all while being immune to the chemical environment in which it works.
As noted above, the degradation of the polishing pad material due to the chemically aggressive nature of the polishing slurry has traditionally been considered problematic. Thus, slurry chemistries and pad compositions resulting in the decomposition of the pad have hitherto been avoided, because such changes would cause the polishing properties of the pad to change drastically as the polishing process progresses, especially during initial exposure of the pad to the slurry. Rapidly changing polishing properties are considered undesirable because the user""s control of the polishing effect on the wafer is lost.
To address this problem, a technique called xe2x80x9cseasoningxe2x80x9d has been widely adopted. Seasoning involves exposing the pad to a conditioning-polishing environment. The pad is attached to a plate, and in the presence of a conditioning slurry, a conditioning ring is used to condition the pad. During this conditioning process, a force is applied to the conditioning ring that mechanically forces the slurry into the pad. The pad is thereby seasoned or conditioned for actual semiconductor wafer processing. While this traditional seasoning technique is somewhat helpful, these prior art processes still suffer from certain disadvantages. For example, even after a pad is conventionally seasoned as mentioned above, the pad""s properties can continue to be transformed, thereby affecting the quality of the wafer""s polished surface.
Accordingly, what is needed in the art is a polishing pad that does not suffer from the disadvantages associated with the prior art processes.
To address the deficiencies of the prior art, the present invention, in one embodiment, provides a polishing pad comprising a polishing body that includes a thermoplastic polymer. The thermoplastic polymer contains a precursor slurry modifier. When the polymer decomposes in the presence of a polishing slurry, the precursor slurry modifier is released to the polishing slurry to form a slurry modifier.
In another embodiment the present invention provides a method for the in situ delivery of a slurry modifier during chemical mechanical polishing of a semiconductor wafer. The method comprises providing a polishing pad comprising a polishing body that includes a thermoplastic polymer. The thermoplastic polymer contains a precursor slurry modifier. The method further comprises adding a polishing slurry and then decomposing the thermoplastic polymer in the presence of the polishing slurry. This releases the precursor slurry modifier to the polishing slurry to form a slurry modifier.
Yet another embodiment provides a polishing apparatus comprising a mechanically driven carrier head, a polishing platen, with the carrier head being positionable against the polishing platen to impart a polishing force against the polishing platen, and the above-mentioned polishing pad attached to the polishing platen.
The foregoing has outlined preferred and alternative features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention.